Elemental copper has been an important metal since ancient times. Recognized desirable attributes of copper include castability, workability, corrosion resistance, and more recently thermal and electrical conductivity. A primary shortcoming of elemental copper relates to machinability. Due to its somewhat gummy nature, copper will at the friction induced elevated temperatures that are encountered during machining clog cutting tools and increase power consumption.
In the past, lead has been added to copper (and copper alloys) to reduce the machinability problem and to provide other desired characteristics. However, recently there has been concern expressed by regulators regarding lead. Lead is already being phased out of the gasoline supply in response to this concern. Now there is a regulatory movement towards requiring reduction and/or removal of lead from brasses that are used to form plumbing conduits.
It is known that bismuth can improve the machinability of copper-containing alloys. See U.S. Pat. Nos. 5,167,726; 5,137,685; and 4,879,094. The disclosure of these patents are incorporated by reference as if fully set forth herein. The above patents teach that when using bismuth relatively high levels of certain elements such as phosphorus, indium, and tin must also be present to offset certain adverse effects of bismuth.
In much of the world, "yellow brass" is relied upon to meet the demands and properties required of cast plumbing products. Yellow brasses typically have 55-70% Cu and 30-45% Zn. Aluminum is often present at below 1.5% and iron is also sometimes present at below 0.5%. Nickel is sometimes present. Trace amounts of S, Mg, Mn, P, As, Se, Te, Sb, Si, Sn, and other elements are also sometimes present in yellow brass (e.g. in certain cases when recycled metal starting materials are used). Plumbing applications require yellow brass alloys that are corrosion resistant, and have good polishability, machinability, strength, and pressure tightness. The brass must also exhibit good castability (freedom from cracks in casting, handling and trimming).
Unfortunately, the art has not yet been able to develop a lead free bismuth yellow brass that is suitable for those plumbing applications where the brass is regularly exposed to water. This is in part due to the tendency of bismuth yellow brasses to dezincify (lose their zinc to the water), with resulting corrosion problems. Thus, a need exists for an improved reduced lead bismuth yellow brass that is useful for plumbing applications.